In the practical use of a vertical axis wind turbine (VAWT) it is highly desirable to have at least first and second substantially vertically spaced bearings. Typically the bearings are radial ball bearings, although others may be utilized. Normally, during use, almost the entire weight of the VAWT is supported by the lowest (i.e. first) bearing. While most bearings, particularly radial ball bearings, can tolerate large radial loads, they do not tolerate axial loading as well, and therefore can wear more quickly than desired during use, causing undesirable downtime of the VAWT, or less than efficient operation.
According to the invention, the problem described above is minimized by providing axial load sharing between at least the first and second (e.g. lower and upper) bearings so that the first bearing does not wear out as quickly. While the load sharing may be anywhere between about 10-90%, ideally the construction is designed so that the load sharing between the first and second bearings (where only two bearings are provided) is roughly about 50-50 so that the bearings wear out at approximately the same time.
While the invention is particularly applicable to VAWTs, under some circumstances the concepts of the invention may be applied to other structures having substantially vertically spaced first and second bearings mounting a shaft for rotation or reciprocation.
In particular, according to one aspect of the present invention there is provided a vertical axis wind turbine assembly comprising: A support. A vertical axis wind turbine having a substantially vertical shaft. At least first, lower, and second, upper, substantially vertically spaced bearings for mounting the shaft for rotation about a substantially vertical axis, the bearings operatively mounted by the support. And a load-sharing assembly operatively connected to the second bearing which allows the bearings to share at least about 10% of the axial load on the bearings. The bearings may be radial ball bearings, or of other conventional types.
Desirably, the load sharing assembly comprises at least one spring (such as a coil or conical spring, although other types are suitable) surrounding an upper portion of the shaft, and operatively engaging the second bearing. Typically, the shaft includes an upper shaft extension, and the load sharing assembly further comprises a spring end cap operatively connected to the upper shaft extension and holding the spring against the second bearing. The spring may consist essentially of a single coil spring, and the spring constant of the spring may be selected with respect to the total axial loading of the bearings so that the bearing load sharing will be roughly about 50-50.
Although a wide variety of different types of VAWTs may be utilized, the vertical axis wind turbine preferably comprises a Savonius wind turbine (e.g. a three bladed Savonius with optimum blade curvature), operatively connected to a utilization device. The support also may have many different configurations, such as a three legged frame having support arms extending radially inwardly from the frame legs and supporting the first and second bearings. While more than two bearings may be provided, the bearings may consist essentially of only the first and second bearings.
According to another aspect of the present invention there is provided a method of operating a vertical axis wind turbine having substantially vertically spaced at least upper and lower bearings by (a) distributing the axial loading between the bearings of the wind turbine so that each of the upper and lower-bearings support at least about 10% (e.g. between about 30-70%) of the total axial load. In the utilization of the method, (a) may be practiced by selecting the spring constant or constants of at least one spring operatively acting on the upper bearing with respect to the total axial load including the weight of the wind turbine.
Since the bearings will wear roughly evenly, the method may further comprise (b) replacing both the upper and lower bearings of the VAWT (especially where it is a Savonius, such as a three-bladed Savonius with optimum blade curvature) at the same time after extended operation thereof. Also, the method may further comprise (c) adjusting the spring constant of, or replacing, the spring without an extended hiatus of operation of the VAWT so as to change the relative load sharing of the bearings depending upon which one is wearing more quickly during operation.
According to still another aspect of the invention, there is provided an assembly comprising: A support. An operable device (not necessarily a VAWT, but any suitable such device) having a substantially vertical shaft. At least first, lower, and second, upper, substantially vertically spaced bearings for mounting the shaft for rotation or reciprocation, the bearings operatively mounted by the support. And a load-sharing assembly operatively connected to the second bearing which allows the bearings to share at least about 10% of the axial load on the bearings. Desirably, the load sharing assembly comprises at least one spring operatively acting on the upper bearing, the spring constant or constants of which is or are selected so that the upper and lower bearings each share about 40%-60% of the total axial load on the bearings. The at least one spring may consist essentially of a single coil or conical spring.
It is the primary object of the present invention to mount a VAWT, or like structure, with at least upper and lower bearings whereby the wear of the bearings is more even than in typical such structures. This and other objects of the invention will become clear from a detailed description of the invention, and from the appended claims.